Head for magnetic recording machines



April 26, 1949.

T. H. LONG HEAD FOR MAGNETIC RECORDING MACHINES Filed Dec. 28, 1945iziarze w.

Patented Apr. 26, 1949 HEAD FOR MAGgTETIC RECORDING MA HINES Thomas H.Long, Elkhart, Ind., assignor to C. G. Conn, Ltd., Elkhart, Ind., acorporation of Indiana Application December 28, 1945, Serial No. 637,656

11 Claims. 1

This invention relates to heads for magnetic recording machines and moreparticularly to the construction of magnetic heads for impressing arecording on a Wire, for playing back a recording from a wire or forerasing a recording from a wire. It will be understood that referencesto a recording machine or a recording head herein are intended toinclude playback or erasing machines or heads and that references to awire are intended to include any elongated magnetic medium whether inthe form of a conventional wire or a tape.

As heretofore constructed, magnetic heads of this type have generallyconsisted of a magnetic core formed with a groove through which the wireruns and having a gap in th core traversed by the wire. It has beenfound in operation of these heads that magnetic mud accumulates on thecore as a gummy residue and tends to shunt the working gap in the core.This mud also holds the wire slightly spaced from the core so that goodmagnetic contact is not obtained between the wire and the core material.These effects ar particularly objectionable at relatively highfrequencies for example, above approximately 2500 cycles per second atwire speeds of about two feet per second and can be avoided only byfrequent and careful cleaning and lubrication of the head.

Another difficulty which has been encountered is that the wire tends toform in the head a slight channel due to the fact that the wire travelsat all times across the same portion of the groove. If there should be asection of wire whose diameter is only slightly in excess of thatpreviously running through the head, binding may occur which will causebreakage of the wire or which will cause cold working of one side of thewire resulting in objectionable kinkiness.

It has further been determined that the flux penetration is a functionof the curvature of the surface to be penetrated so that penetration isless into a concave surface than into a plane surface. Thus a groovedhead has certain inherent magnetic defects.

It is one of the objects of the present invention to provide a head inwhich the several defects in or objections to conventional grooved headsare removed.

It is another object to provide a head which is substantiallyself-cleaning and which in any case can easily be cleaned.

Still another object is to provide a head which is engaged by the wireat different positions along its working gap during operation. This ar-2 rangement, which may be effected by a level-wind device, assists inkeeping the head clean and in preventing channeling of the head by thwire.

Still another object is to provide a head in which the wire leaves thehead in a position of minimum and/ or negligible magnetomotive forcegradient. This arrangement reduces the stray field effect and minimizesdemagnetization of the wire at the point where it leaves the head.

A further object is to provide a head in which the wire runs across asmooth cylindrical surface. In one desired construction, the gap in themagnetic core is filled with a relatively hard nonmagnetic materialjoining smoothly into the core material at opposite sides of the gap.

A still further object is to provide a head formed with a tapered gapacross which the wir may trave1 at different positions to provide aneasy means for varying the effective gap length.

The above and other objects and advantages of the invention will be morereadily apparent from the following description when read in connectionwith the accompanying drawing, in which- Figure 1 is a diagrammatic viewillustrating a head embodying the invention in side elevation;

Figure 2 is a top plan View of Figure 1;

Figure 3 is a partial top plan view of an alternative construction; and

Figure 4 is an end elevation of a head illustrating a modifiedarrangement of the Winding thereon.

Figure 1 illustrates a portion of a more or less conventional magneticrecording machine on an enlarged scale. The machine, as shown, includesa windup spool l0 driven by a suitable power source, not shown, andgeared through gears H to a level-wind device indicated generally at l2.The level-wind device includes a screw 43 for driving a carriage I4 backand forth across the end of the spool. The carriage l4 carries a guideor eyelet 15 through which a wire l6 may be threaded to be Wound evenlyon the spool l0.

Adjacent the level-wind device and on the side thereof remote from thespool a magnetic head is mounted to engage the wire. The head may beeither for magnetizing the wire to impress a recording thereon. forplaying back a recording from the wire or for erasing a previousrecording from the wire. In any case, the head construction will besubstantially identical, it being noted that the same head may be usedfor any of these purposes except that the gap employed in an erasinghead is generally somewhat greater than that in a, recording andplayback head. As

tion to provide increased flux concentration at the point Where the wirecrosses the gap. The body I! is cut away at its upper portion, as bestseen in Figure 2 to expose the laminations adjacent the gap therein sothat they may be en'- gaged by the wire I6, as shown. The showing of thegap in the drawings is exaggerated for ease of illustration, the actualgap on a playback head for a wire speed of two feet per second beingabout .0015 inch.

In order to provide a smooth surface over which the wire IB may travel,the gap is preferably filled with a non-magnetic strip 59. The strip [9is formed of a hard material such, for example, as beryllium copperwhich is hardened to be as hard as, or harder than, the adjacent magnetic material to eliminate the tendency for the wire to drag metalacross the gap from the pole pieces and to eliminate undercutting of thefiller strip by the wire which might occur if a soft material were usedfor the filler strip.

The head may carry a winding of any desired type for recording, playbackor erasing. As shown in Figure 1, a double winding 2! is mounted on thehead on opposite sides of the gap leaving the upper part of the headopen for easy insertion or removal of the wire and for cleaning. Withthe head of the present invention, I have found that the openconstruction, as illustrated in Figure 1, gives results comparable tothose obtained with conventional closed heads although, if desired, aclosed head can be employed by utilizing a winding 22 extending aroundthe gap so that the wire must pass through it, as shown in Figure Onereason for the results obtained with the present head is believed to bethe fact that the wire travels substantially tangentially across the gapand leaves the head in a direction of minimum magnetomotive forcegradient. Therefore, no demagnetization of the wire occurs except thatwhich necessarily occurs immediately after passing the gap.

In operation of the apparatus, as shown in Figures 1 and 2, thelevel-wind device causes the wire to move along the gap in the head asit travels across the gap. This produces a selfcleaning eiiect, tendingto prevent the accumulation of magnetic mud on the head so that the gapwill not be shunted and so that good contact between the wire and themagnetic core is obtained at all times. Since the head construction iscompletely open and does not involve any relatively small grooves inwhich magnetic mud or other foreign material can accumulate, it caneasily be cleaned, simply by wiping the exposed magnetic core materialwith a suitable cleaning agent or solvent. In this way, uniform resultsover a long period of time are obtained with a minimum of attention andwith substantially increased wear life over a conventional grooved head.The advantages of the present construction are particularly pronouncedin the high frequency range.

In the construction of Figure 3, the head is substantially similar tothat of Figures 1 and 2 except that the gap istapered along its length,

as shown. In this construction, a non-magnetic cylindrical frame 23carries magnetic laminations 2a, the ends of which are cut at an angleto provide a tapered gap which may be filled with a tapered non-magneticfiller strip 25. To control the position at which the wire crosses thegap, a guide 26 is provided which can be adjusted transversely of thehead by a screw 27 controlled by a manual handle or crank 28. Byadjusting the position of the guide 26 through the screw 2?, the pointat which the wire crosses the gap can be controlled so that theeffective gap length can easily be varied. This construction may behighly desirable for certain types of work.

While several embodiments of the invention have been shown and describedin detail, it will be understood that these are illustrative only andare not to be taken as a definition of the scope of the invention,reference being had for this purpose to the appended claims.

What is claimed is:

1. A head for a magnetic recording machine comprising a magnetic bodyhaving a substantially smooth convex portion formed with a gap acrosswhich a magnetic wire is adapted to travel, a winding associated withthe body, and guide means engageable with the wire and movable parallelto the gap to guide the wire across different points in the gap length.

2. A head for a magnetic recording machine comprising a magnetic bodyhaving a substantially smooth convex portion formed with a gap acrosswhich a magnetic wire is adapted to travel, a filler of non-magneticmaterial in the gap to provide a smooth surface over which the wire cantravel, a winding on the body, and guide means engageable with the wireand movable parallel to the gap to guide the wire across differentpoints in the gap length.

3. A head for a magnetic recording machine comprising a magnetic bodyhaving a substantially cylindrical portion formed with a gap acrosswhich a magnetic wire is adapted to travel, a winding on the body, and alevel-wind device adjacent the body to move the magnetic wire along thegap as it travels across the gap the gap length being at least as greatas the movement of the wire along the gap by the level wind device.

4. A head for a magnetic recording machine comprising a magnetic bodyhaving a substantially cylindrical portion formed with a gap acrosswhich a magnetic wire is adapted to travel, a filler of non-magneticmaterial in the gap to provide a smooth surface over which the wire cantravel, a

winding on the body, and a level-wind device adjacent the body to movethe magnetic wire along the gap as it travels across the gap, the gaplength being at least as great as the movement of the wire along the gapby the level wind device.

5. A head for a magnetic recording machine comprising a hollowcylindrical body of mag netic material formed with an axially extendinggap in one side across which a magnetic wire is adapted to travel, awinding on the body, and guide means engageable with the wire andmovable parallel to the gap to guide the wire across difierent points inthe gap length.

6. A head for a magnetic recording machine comprising a hollowcylindrical body of magnetic material formed with an axially extendinggap in one side across which a magnetic wire is adapted to travel, anon-magnetic filler in the gap to provide a smooth cylindrical surfaceover which the wire travels, a winding on the body,

and guide means engageable with the wire and movable parallel to the gapto guide the wire across diiferent points in the gap length.

7. A head for a magnetic recording machine comprising a hollowcylindrical body of magnetic material formed with an axially extendinggap in one side across which a magnetic wire is adapted to travel, alevel wind device adjacent the body to move the wire along the gap as ittravels across the gap, and a winding on the body the gap length beingat least as great as the movement of the wire along the gap by the levelwind device.

8. A head for a magnetic recording machine comprising a hollowcylindrical body of magnetic material formed with an axially extendinggap in one side across which a magnetic wire is adapted to travel, anon-magnetic filler in the gap to provide a smooth cylindrical surfaceover which the wire travels, a level wind device adjacent the body tomove the wire along the gap as it travels across the gap, and a windingon the body the gap length being at least as great as the movement ofthe wire along the gap by the level wind device.

9. A head for a magnetic recording machine comprising a series of thinlaminations formed in a substantially cylindrical shape with their endsseparated to form an axially extending gap, the ends of the innerlaminations being separated to a greater extent than the outerlaminations, a level wind device adjacent the head to move a wire alongthe gap as it travels across the gap, and a winding on the laminationsthe gap length being at least as great as the movement of the Wire alongthe gap by the level wind device.

10. A head for a magnetic recording machine comprising a magnetic bodyhaving a substantially cylindrical portion formed with an axiallyextending gap across which a wire is adapted to travel, the gap taperingto provide different gap widths at diiferent points in the gap length, awinding on the body, and adjustable guide means for the wire to guide itacross difierent points in the gap length.

11. A head for a magnetic recording machine comprising partiallycylindrical pole pieces formed with an axially extending gaptherebetween so that a magnetic wire can be moved perpendicular to thegap and can have a component of motion parallel to the gap, a windingmagnetically associated with the pole pieces, and guide means engagingthe wire and movable parallel to the gap to give the wire said componentof motion parallel to the gap.

THOMAS H. LONG.

REFERENCES CITED The following references are of record in the file ofthis patent:

UNITED STATES PATENTS Number Name Date 2,230,913 Schuller i Feb. 4, 19412,351,005 Camras June 13, 1944 FOREIGN PATENTS Number Country Date143,240 Austria Oct. 25, 1935

